1. Field of the Invention
The invention relates to a data compression apparatus for data compressing an n-level information signal, to a data compression method, a transmitter comprising the data compression apparatus, a record carrier having the data compressed audio signal recorded on it in a track of said record carrier, to a data expansion apparatus for data expanding a data compressed n-level information signal, to a data expansion method, and to a receiver comprising the data expansion apparatus.
2. Description of the Related Art
Oversampling delta-sigma data converters are used for high-quality analog-to-digital conversion. Usually, these converters are designed such as to produce a binary, two level digital output signal, also referred to as bitstream or DSD signal. Although it is also possible to design delta-sigma data converters that produce output signals with more than two levels, such converters have not been used in practice because of distortion products and noise caused by non-linearities in such multi-level converters.
Recently, however, a converter has been described for generating a 3-level information signal. Reference is made in this respect to the AES preprint 4443, xe2x80x98A 120 dB dynamic range, 96 kHz, stereo 24-bit analog-to-digital converterxe2x80x99, by K. Leung et al 102nd AES convention (Munich, Germany). The 3-level information signal is available as an internal representation in the converter.
The invention aims at providing an apparatus for enabling data compression of a 3-level, more generally, an n-level information signal, and providing an apparatus for enabling data expansion of the data compressed n-level information signal so as to regain a replica of the original n-level information signal.
The data compression apparatus in accordance with the invention for data compressing an information signal, which is in n-level form, n being larger than 2, comprises
input means for receiving the n-level information signal,
lossless coding means having an input for receiving an input signal, for carrying out a lossless encoding step on the input signal, so as to obtain a data compressed output signal at an output, said lossless encoding means comprising an entropy encoder for carrying out the lossless encoding step on the input signal in response to a probability signal,
prediction means for carrying out a prediction step on the n-level information signal so as to obtain a prediction signal,
probability signal determining means for generating the probability signal in response to said prediction signal, and
output means for supplying said data compressed output signal.
The data expansion apparatus in accordance with the invention for data expanding a data compressed input signal so as to obtain an information signal, which is in n-level form, n being larger than 2, comprises
input means for receiving the data compressed input signal,
lossless decoding means having an input for receiving the data compressed input signal, for carrying out a lossless decoding step on the data compressed input signal, so as to obtain a data expanded output signal at an output, said lossless decoding means comprising an entropy decoder for carrying out the lossless decoding step on the data compressed input signal in response to a probability signal,
output means for supplying said information signal,
prediction means for carrying out a prediction step on the information signal so as to obtain a prediction signal, and
probability signal determining means for generating the probability signal in response to said prediction signal.
By this apparatus, a more efficient storage or transmission of an n-level information signal can be achieved.